The Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard family of communications protocols, such as 802.16d, 802.16e and other variants commonly referred to as WiMAX (Worldwide Interoperability for Microwave Access), works, amongst other frequency bands, in licensed frequency bands, such as 2.3-2.4 GHz and 2.5-2.69 GHz. In some geographical regions/regulatory domains, the WiMAX frequency bands are in close proximity to the 2.4 GHz Bluetooth Industry Scientific and Medical (ISM) band. Consequently, there is considerable residual interference between WiMAX and Bluetooth (victim) and between Bluetooth and WiMAX (victim), which impedes normal reception of the victim communications protocol when the other interfering communications protocol is transmitting. Whilst in some environments, such as laptop platforms, antennae separation between WiMAX and Bluetooth may be relatively high, for example >18 dB, this separation is still not high enough to completely mitigate the interference. Thus, mitigation is needed for these types of interference.
In Bluetooth specification 1.2 and later specifications, Adaptive Frequency Hopping (AFH) is used to improve the performance of physical links in the presence of interference as well as reducing the interference caused by physical links on other devices in the ISM band of 2.4 GHz. When Bluetooth operates in AFH mode, only a subset of all available Bluetooth channels is used by the Bluetooth Master and Bluetooth Slave. When the Bluetooth Master senses interference in the 2.4 GHz ISM band, it adjusts the set of channels to use accordingly. Bluetooth devices that support AFH can operate on as few as 20 out of a total of 79 available channels when restricted by AFH.
Skilled addressees will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the relative dimensions of some of the elements in the figures may be distorted to help improve understanding of embodiments of the present invention.